1. Field of the Invention
This invention relates to a support device for a stent and a method of coating a stent using the device.
2. Description of the Background
Blood vessel occlusions are commonly treated by mechanically enhancing blood flow in the affected vessels, such as by employing a stent. Stents act as scaffoldings, functioning to physically hold open and, if desired, to expand the wall of the passageway. Typically, stents are capable of being compressed, so that they can be inserted through small lumens via catheters, and then expanded to a larger diameter once they are at the desired location. Examples in the patent literature disclosing stents include U.S. Pat. No. 4,733,665 issued to Palmaz, U.S. Pat. No. 4,800,882 issued to Gianturco, and U.S. Pat. No. 4,886,062 issued to Wiktor.
FIG. 1 illustrates a conventional stent 10 formed from a plurality of struts 12. The plurality of struts 12 are radially expandable and interconnected by connecting elements 14 that are disposed between adjacent struts 12, leaving lateral openings or gaps 16 between adjacent struts 12. Struts 12 and connecting elements 14 define a tubular stent body having an outer, tissue-contacting surface and an inner surface.
Stents are used not only for mechanical intervention but also as vehicles for providing biological therapy. Biological therapy can be achieved by medicating the stents. Medicated stents provide for the local administration of a therapeutic substance at the diseased site. Local delivery of a therapeutic substance is a preferred method of treatment because the substance is concentrated at a specific site and thus smaller total levels of medication can be administered in comparison to systemic dosages that often produce adverse or even toxic side effects for the patient.
One method of medicating a stent involves the use of a polymeric carrier coated onto the surface of the stent. A composition including a solvent, a polymer dissolved in the solvent, and a therapeutic substance dispersed in the blend is applied to the stent by immersing the stent in the composition or by spraying the composition onto the stent. The solvent is allowed to evaporate, leaving on the stent surfaces a coating of the polymer and the therapeutic substance impregnated in the polymer.
A shortcoming of the above-described method of medicating a stent is the potential for coating defects. While some coating defects can be minimized by adjusting the coating parameters, other defects occur due to the nature of the interface between the stent and the apparatus on which the stent is supported during the coating process. A high degree of surface contact between the stent and the supporting apparatus can provide regions in which the liquid composition can flow, wick, and collect as the composition is applied. As the solvent evaporates, the excess composition hardens to form excess coating at and around the contact points between the stent and the supporting apparatus. Upon the removal of the coated stent from the supporting apparatus, the excess coating may stick to the apparatus, thereby removing some of the coating from the stent and leaving bare areas. Alternatively, the excess coating may stick to the stent, thereby leaving excess coating as clumps or pools on the struts or webbing between the struts.
Thus, it is desirable to minimize the interface between the stent and the apparatus supporting the stent during the coating process to minimize coating defects. Accordingly, the present invention provides for a device for supporting a stent during the coating application process. The invention also provides for a method of coating the stent supported by the device.
In accordance with one aspect of the invention a support device for a stent is provided. In one embodiment, the support device includes a body having a first end and a second end and at least three sides extending from the first end to the second end, wherein the three sides are capable of penetrating at least partly into one end of a stent. Any of the sides can have a variety of geometrical configurations such as having a radius of curvature or being V-shaped.
In accordance with another embodiment of the invention, an apparatus for supporting a stent during a process of applying a coating material to the stent is provided. The apparatus includes a first member having an end configured to penetrate at least partially in one end of a stent; and a second member having an end configured to penetrate at lease partially in the opposing end of the stent. Each of the ends can comprise two non-parallel sides for allowing the stent to rest on the ends during the process of applying the coating material. A third member can be included and adapted to extend through the stent for connecting the first member to the second member.
In accordance with another embodiment of the invention a device for supporting a stent includes a structure of a variable size so as to allow a section of the structure to penetrate into a first end of the stent until the size of the structure prevents the structure from penetrating deeper into the first end of the stent. The section of the structure that is capable of penetrating into the first end of the stent includes a surface that is in contact with the stent such that the surface that is in contact with the stent does not extend around the entire perimeter of the section.
A second structure of a variable size can also be provide so as to allow a section of the second structure to penetrate into a second, opposing end of the stent until the size of the structure prevents the structure from penetrating deeper into the second end of the stent. The section of the second structure that is capable of penetrating into the second end of the stent includes a surface that is in contact with of the stent such that the surface that is in contact with the stent does not extend around the entire perimeter of the section of the second structure.
In one variation, the second structure is capable of being moved towards or away from the structure for releasably pinching the stent between the structure and the second structure.
In accordance with another aspect of the invention, a method can also be provided for depositing a coating substance on the stent supported by any one the various described embodiments of the present invention. The coating material can be applied by a spray process or by immersing the stent in the coating material. The coating material can comprise a polymer mixed a fluid and optionally a therapeutic substance added thereto.